Sound engineers conventionally mount one or more horn-type loudspeakers above and at the perimeter of the area into which sound is to be provided or reinforced. A universal challenge in such a construction is to provide uniform sound pressure to all portions of the listening area, and often this challenge requires the use of a plurality of loudspeakers even though a single loudspeaker can supply the necessary acoustical power. The use of a plurality of loudspeakers is not only costly, but tends to degrade acoustical performance. Multiple sources of sound result in some locations within the listening area receiving sound from multiple paths, the sound waves from the different paths having undesirable phase differences which can severely degrade performance.
If the listening area is an enclosed auditorium, performance is also degraded by sound reflections from the walls of the auditorium. For this reason, it is necessary for sound engineers to position the loudspeakers used to provide sound to an enclosed auditorium to limit the sound intensity impinging upon the walls of the auditorium to low levels. Often this requirement can only be achieved by use of multiple horn-type loudspeakers even though only a single loudspeaker is required to produce the specified sound level.
It is an object of the present invention to provide a horn-type loudspeaker which may be positioned adjacent to and above a listening area and produces a sound intensity pattern at the listening area which is substantially constant. To achieve this object, a horn-type loudspeaker must produce a sound intensity pattern projecting much more sound energy to the listening areas remote from the loudspeaker than to listening areas adjacent to the loudspeaker.
It is also an object of the present invention to provide a horn-type loudspeaker which produces a sound intensity pattern over an area extending just beyond the border of the listening area, and in the application of this object to a rectangular auditorium, the object is to provide such a horn with a truncated sound intensity pattern. A horn thus constructed is desirable for use in an enclosed rectangular auditorium, since it can be mounted centrally on one end wall above the listening area, or two such horn loudspeakers can be mounted above and centrally of the listening area in back to back relation, the resulting sound pattern being substantially coincident with the listening area. In this manner, the level of projected sound impinging upon the walls of the auditorium is reduced significantly, and performance degrading sound reflections are reduced to low levels.
It is a further object of the present invention to provide a horn-type loudspeaker which simultaneously incorporates all of the foregoing objects. The inventor seeks to provide a horn-type loudspeaker which may be mounted centrally on one wall of a rectangular auditorium above the listening area and project a uniform sound pressure over the listening area limited at its perimeter to the walls of the auditorium.
For auditoriums which are longer than can be serviced by a single loudspeaker, or which require more acoustical energy than can be provided by a single horn-type loudspeaker, the present invention contemplates the use of two loudspeakers constructed according to the present invention mounted in back to back relation above the center of the auditorium. The auditorium can be considered to be two contiguous listening areas, and a single horn-type loudspeaker according to the present invention utilized for each of the listening areas.
It is also an object of the present invention to provide a loudspeaker with two horn structures directed in opposite directions in a single unit which functions in the manner of the two loudspeakers mounted in back to back relation referred to above.
There have been many attempts to control the sound wave propagation of horn-type loudspeakers. U.S. Pat. No. 2,537,141 to Paul W. Klipsch entitled Loud-Speaker Horn discloses a horn-type loudspeaker with controlled angular radiation in which the sound waves expand from the throat of the horn first in one plane and thereafter in the orthogonally related plane. U.S. Pat. No. 4,071,112 to D. Broadus Keele, Jr. entitled Horn Loudspeaker discloses a horn-type loudspeaker with a controlled sound pattern in which the expansion of the sound waves first occurs exponentially from the horn throat, and thereafter conically.
U.S. Pat. No. 4,308,932 to D. Broadus Keele, Jr. entitled Loudspeaker Horn discloses a horn-type loudspeaker for providing sound coverage to a rectangular listening area from an oblique angle, and Keele, Jr. further described his work in a paper entitled A LOUDSPEAKER HORN THAT COVERS A FLAT RECTANGULAR AREA FROM AN OBLIQUE ANGLE given before the Audio Engineering Society Convention, Oct. 8 through 12, 1983. The horn-type loudspeaker of the Keele, Jr. patent and paper varies the horizontal coverage as a function of elevation angle, but provides approximately the same sound energy for all elevational angles, and thus does not generally produce a uniform sound pressure over a rectangular listening area. Even though the remote portions of the listening area are served by sound waves propagated through narrow portions of the horn and the adjacent portions of the listening area are served by sound waves propagated through wider portions of the horn, the concentration of sound energy directed to these remote areas is insufficient to compensate for the loss in sound pressure due to the increase in distance to these remote areas from the horn.